Lubricant and method for lubricating a piston engine



United States Patent O 3,481,873 LUBRICANT AND METHOD FOR LUBRICATING A PISTON ENGINE Robert D. Aylcsworth, Cincinnati, Ohio, assignor to Emery Industries, Inc., Cincinnati, Ohio, a corporation of Ohio No Drawing. Filed Aug. 11, 1967, Ser. No. 659,882 Int. Cl. C10m 3/26, 1/20 US. Cl. 25251.5 5 Claims ABSTRACT OF THE DISCLOSURE A method for lubricating :a piston engine by employing as the lubricant diisotridecyl adipate prepared from the condensation of adipic acid and an oxo alcohol prepared from propylene tetramer. Also, a piston engine lubricant containing said diisotridecyl adipate.

BACKGROUND OF THE INVENTION This invention relates to a lubricant composition and method of use, more particularly to a synthetic ester lubricant especially suited for use in piston engines.

Esters have long been used as lubricating materials. Naturally occurring fats and oils, predominantly glyceride esters, have been used as lubricants for many centuries and more recently synthetic esters or synthetic ester blends prepared from various combinations of mono and polyfunctional acids and alcohols have been developed for lubricant use. The synthetic esters have been used primarily as base stocks for the lubrication of turbine engines. In general, two types of esters have been used as base stocks for turbine engine lubrication: (1) diesters of aliphatic dibasic acids such as adipic acid, azelaic acid or sebacic acid and primary alcohols such as ethylhexanol, isooctanol, isodecanol; and (2) esters of hindered alcohols such as pentaerythritol and trimethylol propane and aliphatic monocarboxylic acids ranging from 5 to carbon atoms in size. Typical diester base stocks for turbine engines include diisoamyl adipate, diethylhexyl adipate, diisooctyl adipate, diethylhexyl azelate, and diethylhexyl sebacate. A summary of the turbine engine synthetic ester lubricants and additives which are available may be found in Synthetic Lubricants, Gunderson and Hart, Reinhold Publishing Corporation, New York, N.Y., 1962.

While synthetic esters have been widely used as turbine engine lubricants, there has been little use made of them in piston engines for many reasons. The problems connected with their acceptance as a piston lubricant have been both economic and technical. From a technical standpoint, synthetic ester lubricants have been unacceptable because those which have been found effective in turbine engines have had a deleterious effect upon the elastomer seals used in piston engines. The turbine engine lubricants have also been found to have excessive volatility and inadequate viscosity properties at high temperatures.

Lubricating compositions used in piston type internal combustion engines, hereinafter referred to as piston engines, must possess special characteristics in order to satisfactorily fulfill the specific requirements placed upon lubricants for this type of engine.

The wide-spread advance of piston engine powered vehicles has lead to the use of piston engine equipment in global areas where ambienttemperature conditions are much more severe than the temperature conditions generally encountered in the temperate climates of the United States and other densely populated areas of the world. Engine oils must now be sufiiciently liquid at temperatures as low as -65 F. to allow the engine to start, yet have volatility properties sufiicient to preclude evaporation 3,481,873 Patented Dec. 2, 1969 when exposed to temperatures near 350 F. over prolonged periods of time.

Petroleum lubricants, which have heretofore been used in piston engines almost exclusively, are generally incapable of providing the high and low temperature requirements when needed today. Petroleum oils can be modified, for example, by addition of kerosene to provide low temperature starting, but when this low temperature modification is effected, the lubricants become too volatile for continued high speed, high temperature operation. Conversely, petroleum oils can be modified so as to provide good high temperature performance, but then the compositions become so viscous at low temperatures that they are unuseable in low temperature environments.

Ester based synthetic oils cover the full operating range of present piston engine requirements. They are liquid enough to allow starting at low temperatures, yet possess volatility characteristics sufliciently low to prevent evaporation at temperatures on the order of 350 F.

While being capable of imparting some improved properties over the petroleum based piston engine oils, the diesters which are commonly used for lubrication of turbine engines such as those referred to above have been found unsuitable for use as piston lubricants because of their excessive volatility and inadequate viscosity properties at high temperatures and most importantly, their tendency to cause elastomers used as seals in automotive engines to swell.

It was thus most surprising that the lubricant of this invention, diisotridecyl adipate, which is prepared using the 0x0 alcohol derived from propylene tetramer, was found to have excellent piston engine lubricating properties in every respect, having none of the drawbacks noted above in connection with either petroleum lubricants or the diesters commonly used in turbine engines. The diisotridecyl adipate ester lubricant of this invention has excellent lubricity, low viscosity at subzero temperatures, low volatility at high temperatures, suitable high viscosity at high temperatures, and a very low order of elastomer swell thus making it well suited for use in piston or Diesel engines. The discovery of the superior lubricant qualities of the synthetic ester of this invention was wholly unexpected in that it has significantly better overall lubricating properties than two well known isomers, di-n-tridecyl adipate and diisotridecyl adipate prepared from the condensation of adipic acid and an oxo alcohol prepared from butyl ene trimer. The most significant advantage of the diisotridecyladipate of this invention over the above-two-noted isomers is in its low temperature performance. While the reasons for the unexpected results using the alcohol derived from propylene tetramer are not fully understood, it is believed that they are attributable to the kind of branching which results from the polymerization of propylene.

DESCRIPTION OF THE INVENTION This invention is concerned with a lubricant composition and a method of lubricating a piston-type engine by employing as a lubricant in said engine a composition comprising as the base fluid an ester prepared from the condensation of adipic acid and an oxo alcohol obtained from propylene tetramer.

The alkanols employed in preparing the esters of this invention may be obtained from the 0x0 process by the catalytic reaction of propylene with carbon monoxide and hydrogen. The reaction occurs at temperatures in the order of 300-400" F., at a pressure in the range of about 1000 to 3000 psi. and in the presence of a suitable catalyst, ordinarily a heavy metal carbonyl, such as cobalt carbonyl. The resulting aldehyde is subsequently hydrogenated to the primary monohydric alcohol, isotridecyl alcohol.

The esterification process .by which isotridecyl adipate is prepared is conveniently effected byheating adipic acid with at least a stoichiometric amount of the i'sotridecyl alcohol prepared in the manner describedtabove. Preferably an excess of about 10 to 100% of the alcohol" is used. The reaction is performed at a temperature of about ISO-230 0., preferably at reflux. Water of esterification is separated. An esterification catalyst such as sulfuric acid may be employed if desired. Also if desired, there may be used a water entrainer, such as a low boiling solvent. When water evolution ceases, esterification is substantially completed and excess alcohol is stripped 01f under vacuum.

As in the use of petroleum lubricants, the diisotridecyl adipate base fluids of this invention must be compounded with certain additives to achieve an engine oil having maximum lubrication capabilities. The' a dditives generally includedetergents, oxidation inhibitors, and metal defactivators. The detergent may bea copolyrner of anacrylic acid ester of a higher fatty alcohol, e.g. lauryl'alcohol and N-vinyl pyrrolidone sold under the trade name Acryloid 966. The detergent is used in amounts of from about 1% to about 5% by weight of the compounded base fluid. The oxidation inhibitor may be such" standard inhibitors as tertiary butyl phenol, phenothiazine or other phenolic or amine antioxidants or combinations thereof.

The metal deactivator may be any of a number of commercial metal deactivators available such as quinizarin (1,4dihydroxyanthraquinone). The metal deactivator is used in amounts of from about 0.005 to about 1% by weight preferably about .005 to about 0.10%.

Other additives such as antifoam agents, silicone, and viscosity index improvers such as acrylate and butylene polymers may be added depending upon the properties which are sought in the lubricant.

The following examples are provided to further illustrate the invention.

EXAMPLE I In order to compare the properties of the ester lubricant of this invention, diisotridecyl adipate in which the alcohol portion is prepared from propylene tetramer, with other similar adipates, the adipates of 2-ethylhexanol and C primary alcohol prepared from propylene trimer by the oxo process were prepared and evaluated as lubricant base stocks. The comparative results obtained are shown Generally, elastomer swell should not exceed 10% in piston engines whereas in aircraft, s'wellof up to to 30% can be tolerated. It may be seen from theabove results that the elastomeric swell of di-Z-ethylhexyl adipate and diisodecyl adipate far exceed tolerable elastomer swell limits while the diisotridecyl adipate had excellent elastomer swell properties. The diisotridecyl adipate is also shown to have superior volatility, viscosity, and flash point characteristics.

EXAMPLE II The viscosity properties of the diisotridecyl adipate lubricant of this invention were measured and compared with isomeric esters prepared from the reaction of adipic acid and normal tridecyl alcohol and the C oxo alcohol made from butylene trimer in order to illustrate the difference between the ester used in the present invention "rived adipic acid ester lubricant with 4 and the isomeric esters. The results are provided in Table Ilbelow.

TABLE II I Adipate of a 0 alcohol derived from- Butylene trimer Adipate of a linear 0 alcohol Propylene tetramer die superior: visdsity properties possessed by thediisotrideEyI adipate 'useain this invention which is formed :from the C alcohol derived from propylene tetramer'. The substantial difference between the adipate of'the Cmalcohol derived from butylene trimer by the oxo process a'nd the adipate of this invention is most Significant and unexpected. Because of. theusimilarity. of structure one would expect their propertiesto siibstan usti't'ridecyl adipate of this inventlon m ts; or can easjl blended with other ester lubricant s with"li"ttle"6r" no sacrifice in its other properties to meet most low temperature specifications. For example, Military Specification MIL-L-l0295A Subzero Internal Combustion Lubricating Oil requires a maximum 'of 8,500 cs. at 40 F. With but a small amount of diluent such as di-Z-ethylhexyl sebacate or any of a number of other ester lubricants, the viscosity ofthe adipicacid esterf'bf a G ggleshol derived from propylene tetrainer via the 6x0 process can be easily lowered to meet the above-noted's'pifibtition. Considerably more diluent is required to achieve desired viscosity properties for the butylene trimer deattendant sacrifice in other desired Properties;

Obviously, many modifications and variations of the invention as hereinbefore set-forth maybemade without departing from the spirit and scope thereof, andtherefore, only those limitations should be imposed as are indicated in the appended claims.

Iclaim: q

1. A method of lubricating a piston engine which comprises applying to said engine as a lubricating agent a composition containing. diisotridecyh adipate formed from adipic acid and a C alcohol derived by the oxo process from propylene tetram'er.

2. The method of claim 1 wherein said lubricating agent contains .a material selected from thegroup ,consisting of an oxidation inhibitor, fa ,detergent ,l;;-a metal deactivator, and mixtures thereof. I

3. A piston engine lubricant comprising a composition containing diisotridecyl adipate formed from adipic acid and a C alcohol derived by the oxo process from propylene tetramer, an oxidation inhibitor, and a metal deactivator for said ester. n p p 4. The composition of claim '3'wh'erein said oxidation inhibitor is selected from the group consisting of phenolic and amine compounds. J

5. The composition of claim" 3 wherein said composition is a blend of diisotridecyl adipate and other synthetic ester lubricants. References Cited v W UNITED STATES Para p ts 3,226,324 12/1965 Eickemeyer. H. 3,249,544 5/1966 Hoffman et al.--...-,..-.,,

FOREIGN PATENTS 1/1955 Great Britain. 7/1966 Great Britain.

DANIEL E. WYMAN, Primary Examiner W. I. SHINE, Assistant Examiner Us. (IL-X3. 252-56 

